After seeing and reading about peoples experiences with using kitty liter pails for panniers, I decided to try something similar with Rubbermaid tubs. Since I built them, I've been using one for commuting to work and I find them fairly convenient compared to the trunk rack that usually I use. I find the tub is easier to pack and easy to carry. It's very simple to carry all my clothes, lunch and supplies in the tub.

What are you using to secure the boxes to the rack? Any stability problems?

I'm using some 2" rope hooks I found at True Value Hardware for less than $1 each. I did push some rubber tubing over the ends of the hooks to keep the hooks from scuffing the rack and to prevent rattling. Currently, I use a bungee cord hooked above the rope hooks and under the bottom support of the rack to keep the tub from bouncing up and off.

I was concerned the tubs might crack at the holes if I connected the hooks directly to the tub so I sandwiched the section of the tub where the hooks are attached between a wooden spacer and a piece of plexiglass. This should spread the weight along the area of the spacers. I'm sure someone else could come up with a much nicer attachment system.

My commute to work is on fairly smooth roads. I haven't had any stability issues - I'm not sure how they'd work on rough pavement or dirt.

Your attachment system will not work on dirt or rough roads, period. I had this problem with the orange MTM drybox that is now on my rack - hard panniers bounce around a lot and WILL fall off if not locked down. I used your exact system and I would lose the box over railroad tracks.

I made a similar set of 'hard' panniers for my Catrike Trail from a couple of plastic ammo cans I got from Cabella's a few years go. Formed some hooks from strap iron and used some screen door springs and a 'beener' to attach the bottom of the box to the rack. Worked pretty smart and kept things dry. I gave them to the new owner of the trike when I swapped it for his Bacchetta. Now I use cheap soft panniers from Amazon.com. I found the ammo can panniers to be a little to heavy, even when empty, to use every day...

I'm guessing that some people might want something more secure for rough roads and several companies that market bicycle bags sell their attachment hardware seperately. Arkel, for example, offers their attachment hardware for saddlebags as a seperate item and in two different sizes.